Study finds bacteria in shower spray

But researchers say not to worry, except maybe about that TB microbe

Published 1:00 am, Tuesday, September 15, 2009

There are some things it is better just not to think about. Like the 10,000 bacteria you inhale with each breath in the average office building. Or the 10 million bacteria in each glass of tap water.

Microbiologists have now added something else to the list of things too gross to contemplate: the deluge of bacteria that hit your face and flow deep into your lungs in the morning shower.

Showers in New York carry a particularly high dose of a microbe related to tuberculosis called Mycobacterium avium. The bacterium and its close cousins can cause a variety of exotic chest complaints, including lifeguard's lung, hot tub lung and Lady Windermere's syndrome.

This unwelcome peek behind the shower curtain has been provided by a group of microbiologists headed by Norman R. Pace of the University of Colorado. As part of a project to measure microbes in the indoor human environment, they looked at shower water, in part because in showers bacteria are incorporated into fine droplets that can be breathed deep into the lungs.

Conventional tests depend on growing cultures of the bacteria to be identified, but because most species cannot be grown in the laboratory, a majority of bacterial species are missed. Pace's method examines the genetic material directly, without the need for culturing bacteria.

He has turned up more than 15 kinds of bacteria in showers across the country, from Tennessee to Illinois, Denver and New York City, he reports this week in The Proceedings of the National Academy of Sciences.

Aside from the thought of being sprayed in the face by a bacterial cocktail every morning, the shower bacteria present no serious danger, with the possible exception of the M. avium. Pace said this microbe could be a risk to people whose immune system was compromised.

The bacteria get into shower heads from the water and build up there, so the dose is highest when the shower is first turned on. Running the water for 30 seconds before stepping in would mean fewer bacteria in one's face, Pace observed. Also, the bacteria seem to find metal shower heads a less hospitable niche than plastic ones.

M. avium tends to be a particular problem in municipal water supplies, Pace said. The reason is that cities treat their water with chlorine, a poison that kills most bacteria but gives avium a selective advantage.

Pace's news for New Yorkers is not all bad. He has also been testing the air in the city's subways. Apart from a lot of aerosolized iron particles, presumably ground off the track by the wheels, the subway air is remarkably fresh and like outdoor air. The reason is that the movement of the trains pumps fresh outdoor air into the tunnels.

Pace explained that his shower and subway projects arose from a grant from the Alfred P. Sloan Foundation in New York, which was interested in how to detect microbes that might be used in a bioterrorist attack.

Pace said he was still taking showers, which he deemed no more dangerous than getting out of bed in the morning.